1. Field of the Invention
The present invention relates to a light guide panel, and more particularly, to a light guide panel capable of uniformly distributing incident light beams from a light source to an entire surface thereof.
2. Description of the Related Art
To date, there have been various types of thin display devices, among which the mainstream has been the Liquid Crystal Displays (LCDs).
The LCDs are applied to various apparatuses including thin wall-mount televisions, notebook computers, monitors for desk-top computers, navigation devices, Personal Digital Assistants (PDAs), mobile phones and game systems. The liquid crystals constituting a display device of the LCD cannot emit light independently and simply transmits or blocks light in response to an electric signal received.
Therefore, in order to display information on the LCD, there is required a separate surface light emitting device, so called a backlight, for lighting the LCD from the back. Such a backlight needs to uniformly irradiate the LCD with high luminance and form a uniform surface light source, which is an important aspect of the quality of the product.
A conventional backlight includes a light source, a light guide panel, a diffusion sheet, a prism and a protective sheet. For its light source, typically a fluorescent lamp such as a Cold Cathode Florescent Lamp (CCFL) or an LED (the LEDs, are widely used for small-size display devices due to their light weight and small size) is used. The light guide panel serves to induce the light beams, from the light source, uniformly upward. The diffusion sheet scatters light to achieve uniform luminance. The prism refracts light vertically and horizontally to collect the light, thereby improving luminance. The protective sheet blocks foreign material from getting in the grooves of the prism and prevents scratch on the surface thereof.
In addition, the light guide panel has a reflecting sheet installed on an underside surface thereof for reflecting the light directed to the bottom of the light guide panel, thereby improving light efficiency. These members are fixed to an LCD substrate in a frame.
Here, the light source emits light toward a side of the light guide panel, and the light guide panel receives the light from the light source through a side thereof to emit light to the front.
Now, the conventional light guide panel will be explained hereunder with reference to the accompanying drawings.
FIG. 1 is a front view illustrating the conventional light guide panel with LEDs disposed next to the light guide panel, and FIG. 2 is an enlarged view illustrating the paths of light from the LED into the light guide panel.
The light guide panel 10, illustrated in FIGS. 1 and 2, has a plurality of LEDs, one of the point light sources, mounted adjacent to a lower edge thereof. The light beams incident from the LED 20 and directed to the side end of the light guide panel 10 are refracted in a predetermined angle due to the refraction difference between the air and the light guide panel 10 and thereby incident into the light guide panel 10. As a result, the incident light beams from the LED 20 form such a distribution in which the light beams incident perpendicular (along a normal line) to the light incident part of the light guide panel have the greatest concentration, and the concentration decreases with the incident angle increasing toward 90 degrees in the left and right with respect to the normal line. That is, the light guide panel 10 is brighter at a portion on the same plane perpendicular to the LED 20 than other portions biased in predetermined angles to the left or right side from the LED 20.
FIG. 3 is a front view of the conventional light guide panel with light beams incident from a plurality of LEDs.
The LED 20 is much smaller than the width of the light guide panel 10, and thus in order to light the entire portion of the light guide panel 10, a plurality of LEDs 20 are disposed at a side of the light guide panel 10, spaced apart in a predetermined interval.
When power is applied to each of the LEDs 20 and light beams are incident into the light guide panel 10, the portions closest to each of the LEDs 20, i.e., the portions directly perpendicular to the LEDs 20 form bright spots 12 whereas the portions farthest to each of the LEDs 20, i.e., the portions diagonally away from the LEDs in the left or right side form dark spots 14.
The alternating bright spots 12 and dark spots 14 hinder uniformity, which is one of the important qualities of the backlight. The LCD manufactured with such a light guide panel 10 has a mixing region, that is not bright uniformly, which refers to a region formed from the light incident surface to a portion where the light beams are evenly mixed, and thus is inadequate for use. The larger mixing region results in a smaller usable portion of the screen.
Needless to say, the LED 20 having the same width as that of the lower end of the light guide panel 10 would solve such a problem of non-uniformity. However, it is difficult to manufacture an LED having such a width corresponding to that of the lower end of the light guide panel 10. Alternatively, a greater number of LEDs 20 can be positioned densely along the light incident surface, which however increases the manufacturing costs.
In an effort to overcome such a problem, a light guide panel, having recesses in the form of concave lenses at a light incident part thereof to diffuse the incident light beams, has been suggested in Korea Patent No. 10-0484536.
However, it is difficult to form a plurality of recesses each having the same dimension at a side of the light guide panel. This configuration widens the incident angle of the incident light beams but renders it difficult to refract the incident light beams toward a width direction of the light guide panel. Therefore, the conventional technology is also limited in enhancing the uniformity of light beams incident into the light guide panel.